What is the role of CT scanning and MRI in the workup of malignant otitis externa (MEO)?

Updated: Apr 13, 2020
  • Author: Brian Nussenbaum, MD, FACS; Chief Editor: Arlen D Meyers, MD, MBA  more...
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Answer

CT scanning and MRI are both useful for evaluating the anatomic extent of soft tissue inflammation, abscess formation, and intracranial complications.

CT scanning fails to diagnose early osteomyelitis because 30-50% of bone destruction is required to detect osteomyelitis by CT scanning.

MRI provides poor bone resolution. The soft tissue manifestations regress on CT scanning and MRI with response to therapy.

Bone changes remain persistently abnormal on CT scans for at least one year and are not well demonstrated by MRI studies. Thus, neither of the tests can be used to determine osteomyelitis resolution.

A retrospective study by Goh et al suggested that MRI findings in skull base osteomyelitis secondary to malignant external otitis (MEO) can help to differentiate the osteomyelitis from advanced nasopharyngeal carcinoma by the presence of a combination of lateral extension, increased T2 signal in adjacent soft tissues, deficiency of architectural distortion, and enhancement equaling or surpassing that of mucosa. [14]

Most authors advocate obtaining a CT scan with the initial evaluation for all patients, whereas Benecke advocates obtaining this test selectively for patients with cranial neuropathy, extensive bone changes on technetium scan, or poor clinical response to treatment. Grandis et al and Okpala et al support obtaining a CT scan early in the diagnostic/treatment algorithm. Peleg et al showed that there is a correlation between clinical course and the extent of anatomical areas involved as measured on initial CT scan findings. [15]

MRI and CT scanning are equally sensitive in detecting the soft tissue extent of the disease, but MRI is more sensitive for detecting intracranial complications.

A retrospective clinical study investigated the prognostic value of serial temporal bone MRI follow-up patterns in patients with necrotizing otitis externa. The most common finding was retrocondylar fat infiltration, which was also the earliest change seen. The patients with combined extension patterns (50%) had significantly lower overall survival compared with the patients with limited extension patterns or single extension patterns, suggesting that combined extension patterns, versus single or limited extension patterns, may be a poor prognostic factor in patients with necrotizing otitis externa. [16]


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